General principles of attraction and competitive attraction as revealed by large-cage studies of moths responding to sex pheromone.

Knowledge of how insects are actually affected by sex pheromones deployed throughout a crop so as to disrupt mating has lacked a mechanistic framework sufficient for guiding optimization of this environmentally friendly pest-control tactic. Major hypotheses are competitive attraction, desensitization, and camouflage. Working with codling moths, Cydia pomonella, in field cages millions of times larger than laboratory test tubes and at substrate concentrations trillions of times less than those typical for enzymes, we nevertheless demonstrate that mating disruption sufficiently parallels enzyme (ligand) -substrate interactions so as to justify adoption of conceptual and analytical tools of biochemical kinetics. By doing so, we prove that commercial dispensers of codling moth pheromone first competitively attract and then deactivate males probably for the remainder of a night. No evidence was found for camouflage. We generated and now validate simple algebraic equations for attraction and competitive attraction that will guide optimization and broaden implementation of behavioral manipulations of pests. This analysis system also offers a unique approach to quantifying animal foraging behaviors and could find applications across the natural and social sciences.

Toxicity of bloodmeals from ivermectin-treated cattle to Anopheles gambiae s.l.

Two anthelmintic drugs used as cattle dewormers, ivermectin and moxidectin, were tested for their lethal and sublethal effects on the malarial vectors Anopheles gambiae s.s. and An. arabiensis. In the laboratory, direct addition of ivermectin to bovine blood reduced the survivorship and fecundity of mosquitoes fed on the blood. The median lethal concentration (LC(50)) of ivermectin in the bloodmeal, for the laboratory populations of An. gambiae s.l., was 19.8 ppb. In the field, commercially available formulations containing ivermectin or moxidectin were injected into cattle at three times the recommended dose. Most (90%) of the An. gambiae s.s. that fed on the ivermectin-treated cattle within 2 weeks of treatment failed to survive more than 10 days post-bloodmeal. No eggs were deposited by An. gambiae s.s. that fed on ivermectin-treated cattle within 10 days of treatment. In contrast, the survivorship and egg production of the mosquitoes that fed on the moxidectin-treated cattle were no different from those feeding on untreated cattle. These results indicate that treatment of cattle with ivermectin could be used, as part of an integrated control programme, to reduce the zoophilic vector populations that contribute to the transmission of the parasites responsible for human malaria.

Designation of chemicals in terms of the locomotor responses they elicit from insects: an update of Dethier et al. (1960).

A scheme updating that of Dethier et al. (1960) (J. Econ. Entomol. 53: 134-136) for chemicals influencing insect locomotor behavior is introduced. Attractant, repellent, and arrestant retain their previous definitions. However, attractants or repellents are now recognized to operate both by kinetic and tactic mechanisms. Locomotor initiator is a new term for stimuli that activate normal levels of kinetic locomotion. Locomotor stimulant is reserved for activation of abnormally high kinetic locomotion, like that arising upon sublethal exposure to certain insecticides. The new terms engagent and disengagent apply to chemicals that, by their effects on locomotion, increase or decrease interaction with the source of stimulation, respectively. With these clarifications, insect behavioral terms unique to medical entomology but contradicting Dethier et al.'s classical scheme can be reconciled with the vocabulary of formal behavioral science.